Hygrothermal properties of unfired earth bricks: Effect of barley straw, hemp shiv and corn cob addition

• Published in: Energy and buildings 2018-11, Vol.178, p.265-278
• Main Authors: Laborel-Préneron, A., Magniont, C., Aubert, J-E.
• Format: Article
• Language: English
• Subjects: Aggregates; Air quality; Barley; Barley straw; Building materials; Civil Engineering; Construction materials; Corn; Earth; Earth brick; Energy conversion efficiency; Energy efficiency; Engineering Sciences; Formulations; Heat conductivity; Heat transfer; Hemp; Hygrothermal performance; Indoor air pollution; Indoor environments; Insulation; Materials; Mathematical analysis; Moisture Buffer Value; Permeability; Plant aggregate; Properties (attributes); Saline solutions; Sorption; Sorption–desorption isotherm; Specific heat; Specific heat capacity; Straw; Thermal conductivity; Thermal insulation; Water vapor; Water vapour permeability; Weight
• ISSN: 0378-7788; 1872-6178
• DOI: 10.1016/j.enbuild.2018.08.021

•Thermal conductivity decreases with the addition of plant aggregates.•Earth material is highly water vapour permeable.•Sorption–desorption isotherms are assessed with DVS and saturated salt solution methods.•MBV of earth-based materials is excellent. Earth is a material presenting good hygric properties, which is an important point as comfort and indoor air quality have become major issues. Nowadays, the energy efficiency of a construction is also crucial, but the thermal insulation provided by an earth brick is quite low. Therefore, some plant aggregates were added to lighten the material, thus decreasing its thermal conductivity. The hygrothermal properties of seven formulations made of earth with 0, 3 or 6% by weight content of barley straw, hemp shiv or corn cob were assessed. The properties determined were thermal conductivity, specific heat capacity, water vapour permeability, and sorption–desorption isotherms measured with the saturated salt solution and DVS methods. The theoretical MBV was also calculated. The study showed a large decrease in thermal conductivity when a large volume of plant aggregates was added while plant aggregates incorporation conversely affected the thermal inertia parameters. Concerning water vapour permeability, as earth is a very permeable material, the addition of plant aggregates did not improve this property. The sorption capacity of bio-based earth materials was slightly increased in comparison with earth alone. Finally, the calculated MBV showed the excellent buffering capacity of this kind of material, with and without plant aggregates.